An arrangement for influencing liquid flow and a method

ABSTRACT

According to the present disclosure there is provided an arrangement for influencing liquid flow, the arrangement comprising: a first section selectively configurable to provide a vortex generator surface to induce vortices in the liquid flow. The arrangement further comprises a second section, wherein the first section and second section are movable relative to one another to provide the vortex generator surface.

The present disclosure relates to arrangements and duct arrangements forinfluencing fluid flow, or specifically liquid flow, and associatedcrafts and methods.

BACKGROUND

Aircraft and watercraft comprise components which are exposed to, ormake use of, fluid flows. Certain components are configured to interactwith, including guide, the fluid flows to facilitate the production ofthrust or lift. Increasing or maintaining the magnitude of thrust orlift produced, whilst using an equivalent or lower quantity of fuel, isimportant in reducing carbon emissions. Thus, techniques for improvingfluid interaction with craft components are of interest in the field.

The interaction of craft components with fluid flows results in a regionof disturbed flow (often turbulent) downstream of the craft, known as awake. Often, craft must maintain a safe distance so as not to bedisturbed by the wake. Techniques for reducing or otherwise influencingthe wake are of interest in the field.

The interaction of craft components with fluid flows results in noise.Techniques for reducing or otherwise influencing the noise are ofinterest in the field, for example to reduce disturbance to aquatic lifein the field of watercraft, or to reduce environmental noise in thefield of aircraft.

It is an object of the present invention to provide an improved and/ormethod thereof and/or address one or more of the problems discussedabove, or discussed elsewhere, or to at least provide an alternativesystem and/or method.

SUMMARY OF THE INVENTION

According to the present invention there is provided arrangements andmethods as set forth in the appended claims. Other features of theinvention will be apparent from the dependent claims, and thedescription which follows.

According to a first aspect of the present invention there is provided aduct arrangement for influencing fluid flow, the duct arrangementcomprising: a first duct section arranged to receive a fluid flowtherethrough, the first duct section defining a first direction throughthe first duct section from a fluid inlet end to a fluid outlet end; asecond duct section defining a second direction through the second ductsection from a fluid inlet end to a fluid outlet end, the second ductsection comprising a vortex generator surface, wherein the vortexgenerator surface is arranged to induce vortices in the fluid flowthrough the first duct section.

Duct sections are advantageous in guiding fluid flows and housingcomponents. The provision of a vortex generator surface is beneficial inreducing and/or minimising the magnitude of a wake induced by the ductsections. The vortex generator surface also improves the properties ofthe fluid flow, such that interaction with, for example, a subsequentrotor results in improved rotor efficiency and/or thrust production. Inone example, the vortex generator surface may be configured to interactwith a fluid flow to induce vortices such that the properties of fluidflow comprises a vorticity magnitude. In one example, the duct sectionsinteract with the fluid flow to induce a first set of fluid properties,and the vortex generator surface interacts with the fluid flow to inducea second set of fluid properties. The second set of fluid properties maycomprise an increase in vorticity magnitude of the fluid flow.Surprisingly and advantageously, in this way, the vorticity magnitude ofthe wake is reduced.

A duct section may be a hollow cylinder, tube or ring. A duct sectionmay be a section, or region, of a larger duct, cylinder, tube or ring.The duct cross-section may be of any shape, for example square orrectangular, but is typically arcuate, for example circular orelliptical.

In one example, the vortex generator surface is configured to induce aplurality of spaced apart vortices. The spatial separation of thevortices may correspond to the form of the vortex generator surface. Theplurality of vortices may be periodic. In one example, the vortexgenerator surface comprises a series of projections. In one example, theprojections are serrations and/or undulations. In one example, theprojections may comprise a length and a height. The length may extendbetween the sides of the projection. The series of projections may bealigned substantially side by side. That is, the projections may belaterally aligned. The projections may be only laterally aligned, forexample extending only in one dimension or direction (e.g. along a line,edge or curve), and not forming an array extending in or distributedacross a 2D surface. The projections may be curved along their length.In one example, the spatial separation of the vortices may beproportional to the spatial separation of the projections. In oneexample, each projection is configured to induce a vortex in the fluidflow.

The projections may project in a direction substantially opposite to thefirst direction. That is, the height may be parallel to the firstdirection, and the projections may comprise a base and a tip, thedirection from the base to the tip being substantially opposite to thefirst direction. The bases of the projections may be laterally aligned.The series of projections may form an at least partially continuouswave-like profile. That is, a wave maybe formed, which may be curved orsawtooth or chevron like. The projections maybe adjacent to one another,such that there is no gap between the projections. It has been foundthat an at least partially continuous wave-like profile of laterallyaligned projections is a highly advantageous configuration ofprojections for inducing vortices in the fluid flow.

In one example, the vortex generator surface is a ring, or otherwise hasa similar cross-sectional profile to the duct sections. In this way, avortex generator surface can be provided that has a similarcross-sectional profile to the duct sections. This is advantageous forinducing vortices in the fluid flow through the first duct section.

In one example, the second duct section is attached to, supported byand/or is formed integrally with, the first duct section. The secondduct section and the first duct section may be one single integrallyformed unit. Alternatively, the second duct section and first ductsection may be separate parts configured to be assembled to form asingle unit.

In this way, the second duct section may be attached to an existingfirst duct section, for example by a retrofit process. In this way, avortex generator surface can be provided on an existing first ductsection. Alternatively, the first and second duct sections can beprovided as an integrally formed unit. The vortex generator surface canthereby be located at an optimal position for interacting with the fluidflow. Furthermore, this construction results in a robust ductarrangement.

In one example, the second duct section is aligned with and/or iscoaxial with the first duct section.

Advantageously, in this way, the second duct section, and thus thevortex generator surface, is well positioned to interact and influencethe fluid flow to induce vortices in the fluid flow through the firstduct section.

In one example, the duct arrangement further comprises a rotor housed inthe first duct section.

Rotors can be used to generate power and/or propulsion. The ductarrangement including a rotor improves the rotor efficiency and alsoleads to a reduction in the magnitude of the wake produced by the rotor.In one example, the rotor is a propeller and/or turbine rotor.

In one example, the second duct section is provided upstream of thefirst duct section along the first direction.

In this way, the first duct section and second duct section areseparated along the first direction. The vortices induced by the vortexgenerator surface thereby pass downstream to the first duct section.This is advantageous in reducing the wake induced by the duct sections.This is also advantageous in reducing the wake induced by any componentshoused in the duct section, such as a rotor, and also improving rotorefficiency.

In one example, the second duct section is provided at a leading edge ofthe first duct section. In one example, the vortex generator surface isprovided at a leading edge of the first duct section.

In this way, improved interaction with the fluid flow is facilitated.Moreover, in this way, vortices of an advantageous orientation arethereby induced. Furthermore, the vortex generator surface may interactwith the fluid flow prior to any surfaces downstream. The vorticesinduced by the vortex generator surface can subsequently passdownstream, where the vortices present in the fluid flow canadvantageously interact with downstream components to improve theirefficiency and/or reduce the magnitude of the wake.

In one example, the second duct section is provided upstream of therotor along the first direction.

Advantageously, the vortices induced in the fluid flow are incident onthe rotor and interact with the wake produced by the rotor. It has beenfound that this has the effect of improving the level of thrust orpropulsion produced by the rotor. Additionally, this also results in anadvantageous reduction in the magnitude of the wake structure trailingthe craft.

In one example, the projections of the vortex generator surface projectin a direction substantially opposite to the first direction.

In this way, improved interaction with the fluid flow is facilitated.Moreover, in this way, vortices of an advantageous orientation arethereby induced.

In one example, the first duct section interacts with the fluid flow toinduce a first set of fluid properties, and the vortex generator surfaceinteracts with the fluid flow to induce a second set of fluidproperties, the second set of fluid properties comprising an increase inthe vorticity magnitude of the fluid flow. Surprisingly andadvantageously, this facilitates a reduction in the vorticity magnitudeof the wake.

In one example, the vortex generator surface is configured to induce aplurality of spatially separated vortices in the fluid flow, optionallyperiodic vortices. Spatially separated vortices are beneficial inreducing vorticity magnitude of the wake and also in reducing drag.

According to a second aspect of the present invention there is providedan aircraft or watercraft comprising a duct arrangement according to thefirst aspect of the present invention.

Aircraft includes aeroplanes, helicopters, unmanned aerial vehicles, orother machines capable of flight. Watercrafts include boats, ships andhovercraft, unmanned water-based vehicles, including those capable ofunderwater operation. Watercrafts also include floating platforms, suchas oil rigs, with propulsion or energy generating capabilities by virtueof rotors.

According to a third aspect of the present invention there is provided amethod of influencing fluid flow, the method comprising: generatingvortices in a fluid flow using a second duct section comprising a vortexgenerating surface; and receiving the fluid flow in a first ductsection.

According to a fourth aspect of the present invention there is providedan arrangement for influencing liquid flow (as opposed to air flow), thearrangement comprising: a first section selectively configurable toprovide a vortex generator surface to induce vortices in the liquidflow.

Such an arrangement is highly advantageous in improving the efficiencyof watercraft propulsion systems, and additionally in reducing themagnitude of the wake created by watercraft. Selective configuration ofthe vortex generator surface allows said surface to be provided onlywhen necessary or desired, or to a necessary or desired extent ordegree.

In one example, the arrangement further comprises: a second section,wherein the first section and second section are movable relative to oneanother to provide the vortex generator surface.

In this way, the vortex generator surface need not always be provided,or may be movable to a specific location for increased or decreasedinteraction with the fluid flow. This is beneficial in inducing vorticesin the liquid flow only when necessary or desired, or to a necessary ordesired extent or degree.

In one example, the vortex generator surface may be configured tointeract with a liquid flow to induce vortices such that the propertiesof liquid flow comprises a vorticity magnitude. In one example, othersurfaces of the arrangement interact with the liquid flow to induce afirst set of liquid properties, and the vortex generator surface, whenprovided, interacts with the liquid flow to induce a second set ofliquid properties. The second set of liquid properties may comprise anincrease in vorticity magnitude of the liquid flow. Surprisingly andadvantageously, in this way, the vorticity magnitude of the wake isreduced.

In one example, the first section is movable away from and/or toward thesecond section, for example, wherein the first section is extendablefrom and/or retractable into the second section. That is, thearrangement may be a telescopic or sleeve-like arrangement.

In this way, the profile of the arrangement when the vortex generatorsurface is not provided may be minimised.

In one example, the first section is selectively configurable to providethe vortex generator surface at a leading edge of the second section.

In this way, the vortex generator surface may interact with the liquidflow prior to any surfaces downstream. The vortices induced by thevortex generator surface can subsequently pass downstream, where thevortices present in the liquid flow can advantageously interact withdownstream components to improve their efficiency and/or reduce themagnitude of the wake.

In one example, the second section comprises a flow control surface, forexample a fin, rudder, duct and/or rotor, and/or is a flow controlsurface.

Flow control surfaces in watercraft generate wake, and inducing vorticeswhich interact with the flow control surfaces can advantageously resultin a reduction in magnitude of the resulting wake. In one example, flowcontrol surfaces interact with the liquid flow to induce a first set ofliquid properties, and the vortex generator surface, when provided,interacts with the liquid flow to induce a second set of liquidproperties. The second set of liquid properties may comprise an increasein vorticity magnitude of the liquid flow. Surprisingly andadvantageously, in this way, the vorticity magnitude of the wake isreduced.

In one example, the arrangement further comprises a controller arrangedto implement the selective configuration of the vortex generatorsurface.

Providing a controller facilitates an automated arrangement, and or anarrangement which is configurable based on variables monitored by thecontroller.

In one example, the controller is arranged to implement the selectiveconfiguration of the vortex generator surface in dependence upon: a usercommand, input from a sensor arrangement (local to or remote from thearrangement) and/or one or more environmental conditions.

Selective configuration of the vortex generator surface may thereby beimplemented only when necessary or desired, and based on appropriatefeedback or control.

Alternatively, selective configuration of the vortex generator surfacemaybe somewhat passive, for example moving to a particular configurationwhen liquid properties force this change (e.g. with appropriate liquidpressure, temperature, salinity, flow rate, and so on).

In one example, the first section is selectively configurable to changethe shape of the arrangement, thereby to provide the vortex generatorsurface to induce vortices in the liquid flow. In one example, the firstsection is selectively configurable to change the shape of the vortexgenerator surface. In one example, the first section is selectivelyconfigurable to change the shape of the vortex generator surface,thereby to provide the vortex generator surface to induce vortices inthe liquid flow.

Advantageously, a first shape of the arrangement, without the vortexgenerator surface provided, may be optimised for a certain operationalcharacteristic, whereas a second shape of the arrangement, with thevortex generator surface provided, may be optimised for propulsionefficiency and/or wake reduction. Additionally, altering the shape ofthe vortex generator surface is advantageous for improving thepropulsion efficiency to a certain degree, or reducing the wakemagnitude by a required or desired amount.

In one example, the first section is selectively configurable in: afirst configuration wherein the vortex generator surface is provided toinduce vortices with a first property in the liquid flow; and a secondconfiguration wherein the vortex generator surface is provided to inducevortices with a second property in the liquid flow.

In one example, the second property is greater than the first property,for example, wherein the first property is a magnitude of zero and thesecond property is a non-zero magnitude, or wherein the first propertyis a non-zero magnitude and the second property is a greater non-zeromagnitude.

In one example, the first section is selectively configurable to providea vortex generator surface comprising a series of projections. In oneexample, the projections are serrations and/or undulations. In oneexample, the projections may comprise a length and a height. The lengthmay extend between the sides of the projection. The series ofprojections may be aligned substantially side by side. That is, theprojections may be laterally aligned. The projections may be curvedalong their length.

In one example, the first section is selectively configurable to providea vortex generator surface to induce a plurality of spatially separatedvortices in the fluid flow, optionally periodic vortices. Spatiallyseparated vortices are beneficial in reducing vorticity magnitude of thewake and also in reducing drag.

According to a fifth aspect of the present invention there is provided awatercraft comprising an arrangement according to the fourth aspect ofthe present invention.

Watercrafts include boats, ships and hovercraft, unmanned water-basedvehicles, including those capable of underwater operation. Watercraftsalso include floating platforms, such as oil rigs, with propulsion orenergy generating capabilities by virtue of rotors

According to a sixth aspect of the present invention there is provided amethod of influencing liquid flow in an arrangement comprising a firstsection selectively configurable to provide a vortex generator surface,the method comprising: configuring the first section to provide thevortex generator surface to induce vortices in the liquid flow.

According to a seventh aspect of the present invention there is providedan arrangement for influencing fluid flow, the arrangement comprising: afirst section selectively configurable to provide a vortex generatorsurface, the vortex generator surface comprising a series of laterallyaligned projections, to induce vortices in the fluid flow.

Laterally aligned projections are a highly advantageous construction forinducing vortices in a fluid flow. Selective configuration of the firstsection to provide a vortex generator surface enables the vortexgenerator surface to be provided only when necessary or desired.

Laterally aligned may be alternatively defined or described as theprojections extending only in one dimension or direction (e.g. along aline, edge or curve), and not forming an array extending in ordistributed across a 2D surface. Again, this arrangement may beadvantageous in certain applications, for example in terms of inducingvortices in a liquid flow.

In one example, the vortex generator surface may be configured tointeract with a fluid flow to induce vortices such that the propertiesof fluid flow comprises a vorticity magnitude. In one example, the firstsection interacts with the fluid flow to induce a first set of fluidproperties, and the vortex generator surface, when provided, interactswith the fluid flow to induce a second set of fluid properties. Thesecond set of fluid properties may comprise an increase in vorticitymagnitude of the fluid flow. Surprisingly and advantageously, in thisway, the vorticity magnitude of the wake is reduced.

In one example, the projections are serrations and/or undulations. Inone example, the projections may comprise a length and a height. Thelength may extend between the sides of the projection. Laterally alignedmay mean that the series of projections are aligned substantially sideby side. The projections may be curved along their length.

The projections may comprise a base and a tip. The bases of theprojections may be laterally aligned. The series of projections may forman at least partially continuous wave-like profile. That is, a wavemaybe formed, which maybe curved or sawtooth or chevron like. Theprojections maybe adjacent to one another, such that there is no gapbetween the projections. It has been found that an at least partiallycontinuous wave-like profile of laterally aligned projections is ahighly advantageous configuration of projections for inducing vorticesin the fluid flow.

In one example, the arrangement further comprises: a second section,wherein the first section and second section are movable relative to oneanother to provide the vortex generator surface.

In this way, the vortex generator surface need not always be provided,or may be movable to a specific location for increased or decreasedinteraction with the fluid flow. This is beneficial in inducing vorticesin the liquid flow only when necessary or desired.

In one example, the first section is movable away from and/or toward thesecond section, for example, wherein the first section is extendablefrom and/or retractable into the second section.

In this way, the profile of the arrangement when the vortex generatorsurface is not provided may be minimised.

In one example, the first section is selectively configurable to providethe vortex generator surface at a leading edge of the second section.

In this way, improved interaction with the fluid flow is facilitated.Moreover, in this way, vortices of an advantageous orientation arethereby induced. Furthermore, the vortex generator surface may interactwith the fluid flow prior to any surfaces downstream. The vorticesinduced by the vortex generator surface can subsequently passdownstream, where the vortices present in the fluid flow canadvantageously interact with downstream components to improve theirefficiency and/or reduce the magnitude of the wake.

In one example, the second section comprises a flow control surface, forexample a fin, rudder, duct and/or rotor, and/or is a flow controlsurface.

Flow control surfaces in an aircraft and watercraft generate wake.Inducing vortices which interact with the flow control surfaces canadvantageously result in a reduction in magnitude of the resulting wake.

In one example, the arrangement further comprises a controller arrangedto implement the selective configuration of the vortex generatorsurface.

Providing a controller facilitates an automated arrangement, and or anarrangement which is configurable based on variables monitored by thecontroller.

In one example, the controller is arranged to implement the selectiveconfiguration of the vortex generator surface in dependence upon: a usercommand, input from a sensor arrangement (local to or remote from thearrangement) and/or one or more environmental conditions.

Selective configuration of the vortex generator surface may thereby beimplemented only when necessary or desired, and based on appropriatefeedback or control.

Alternatively, selective configuration of the vortex generator surfacemay be somewhat passive, for example moving to a particularconfiguration when liquid properties force this change (e.g. withappropriate liquid pressure, temperature, salinity, flow rate, and soon)

In one example, the arrangement comprises an actuator assembly operableto provide the vortex generator surface. An actuator may be mechanical(e.g. a piston) or fluidic (using the movement of fluid, or using fluidpressure, to shape the surface).

The provision of actuators to provide the vortex generator surfaceensures robust and reliable control of the vortex generator surface.Selective configuration of the vortex generator surface may thereby beimplemented by control of the actuator assembly to provide the vortexgenerator surface only when necessary or desired.

In one example the first section comprises: a resilient membrane; theactuator assembly operable to adjust the profile of the resilientmembrane to provide the vortex generator surface.

A resilient membrane has a smooth profile, which assists in reducingdrag. Moreover, the profile of the resilient profile can be manipulatedto provide a vortex generator surface of a particular shape which isadvantageous to achieve a necessary or desired level of reduction in themagnitude of the wake and/or improvement in rotor efficiency.

In one example, the first section is formed from a shape memory alloy.

Shape memory alloys can repeatedly be reshaped to provide a vortexgenerator surface of a desired shape. In this case, an actuator assemblymay not be necessary, increasing the reliability of provision of thevortex generator surface, and simplifying construction.

In one example, the first section is selectively configurable in: afirst configuration wherein the vortex generator surface is provided toinduce vortices with a first property in the fluid flow; and a secondconfiguration wherein the vortex generator surface is provided to inducevortices with a second property in the fluid flow.

In one example, the second property is greater than the first property,for example, wherein the first property is a magnitude of zero and thesecond property is a non-zero magnitude, or wherein the first propertyis a non-zero magnitude and the second property is a greater non-zeromagnitude.

In one example, the first section is selectively configurable to providea vortex generator surface to induce a plurality of spatially separatedvortices in the fluid flow, optionally periodic vortices. Spatiallyseparated vortices are beneficial in reducing vorticity magnitude of thewake and also in reducing drag.

According to an eighth aspect of the present invention there is providedan aircraft or watercraft comprising an arrangement according to seventhaspect of the present invention.

Aircraft includes aeroplanes, helicopters, unmanned aerial vehicles, orother machines capable of flight. Watercrafts include boats, ships andhovercraft, unmanned water-based vehicles, including those capable ofunderwater operation. Watercrafts also include floating platforms, suchas oil rigs, with propulsion or energy generating capabilities by virtueof rotors.

According to a ninth aspect of the present invention there is provided amethod of influencing fluid flow in an arrangement comprising a firstsection selectively configurable to provide a vortex generator surfacecomprising a series of laterally aligned projections, the methodcomprising: configuring the first section to provide the vortexgenerator surface to induce vortices in the fluid flow.

Any aspect of the present invention described above may comprise any orall features of any or all other aspects of the present invention, asdesired or as appropriate. This will be clear to the skilled person fromtheir own knowledge, and the clearly closely linked nature of allaspects and embodiments discussed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, and to show how embodimentsof the same may be carried into effect, reference will now be made, byway of example only, to the accompanying diagrammatic drawings in which:

FIG. 1 shows a perspective view of a duct;

FIG. 2 shows a perspective view of a duct arrangement according to anexemplary embodiment;

FIG. 3 shows an enlarged view of the duct arrangement of FIG. 2 ;

FIG. 4 shows a perspective view of an arrangement according to anexemplary embodiment in a first configuration;

FIG. 5 shows the arrangement of FIG. 4 in a second configuration;

FIG. 6 shows interaction of the duct of FIG. 1 with a fluid flow;

FIG. 7 shows interaction of the duct arrangement of FIG. 2 with a fluidflow;

FIG. 8 shows interaction of the duct of FIG. 1 with a fluid flow;

FIG. 9 shows interaction of the duct arrangement of FIG. 2 with a fluidflow; and

FIGS. 10, 11 and 12 show methods according to exemplary embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1 , a duct 1 is shown. The duct 1 is a hollowcylinder, tube, or ring. In this example, the duct 1 is for housing, orotherwise surrounding, a rotor. In one exemplary embodiment, the rotoris a propeller rotor. In another exemplary embodiment, the rotor is aturbine rotor.

Referring to FIGS. 2 and 3 , a duct arrangement 100 is shown. The ductarrangement 100 is for installation in an aircraft or watercraft. Theduct arrangement comprises a first duct section 1000 which is of asimilar or identical construction to duct 1. That is, the first ductsection 1000 is a hollow cylinder, tube, or ring. The first duct section1000 is for housing, or otherwise surrounding, a rotor.

The first duct section 1000 is arranged to receive a fluid flowtherethrough. The first duct section 1000 comprises a fluid inlet end1002 and a fluid outlet end 1004. The fluid inlet end 1002 is afrontward or leading end of the first duct section 1000. The fluidoutlet end 1004 is a rearward or trailing end of the first duct section1000. The first duct section 1000 defines a first direction (indicatedby arrow 1006) through the first duct section 1000 from the fluid inletend 1002 to the fluid outlet end 1004.

The duct arrangement 100 further comprises a second duct section 2000.The second duct section 2000 comprises a fluid inlet end 2002 and afluid outlet end 2004. The fluid inlet end 2002 is a frontward, leading,end of the second duct section 2000. The fluid outlet end 2004 is arearward, trailing, end of the second duct section 2000 and opens intothe fluid inlet end 1002 of the first duct section 1000. The second ductsection 2000 defines a second direction (indicated by arrow 2006)through the second duct section 2000 from the fluid inlet end 2002 tothe fluid outlet end 2004. The second duct section 2000 is providedupstream of the first duct section 1000 along the first direction 1006.The second duct section 2000 is provided at the leading edge of thefirst duct section 1000. Where the first duct section 1000 houses arotor, the second duct section 2000 is provided upstream of the rotoralong the first direction 1006.

The first duct section 1000 and second duct section 2000 are radiallyand circumferentially aligned (e.g. the circumferences are substantiallythe same and are aligned) and are coaxial. In this manner, the firstdirection 1006 is substantially parallel to, and substantially alignedwith, the second direction 2006.

In some embodiments, the first duct section 1000 and second duct section2000 are separately formed. Each duct section is formed from a materialwell-suited to the application in question, and might typically beformed from a polymer, a metal, and so on. The first duct section 1000and second duct section 2000 are bolted, adhered or otherwise fixedtogether and are thereby connected or attached. In this way, the secondduct section 2000 is supported by the first duct section 1000. In oneembodiment, the second duct section 2000 is provided in portions of ductsection and each portion is bolted to the first duct section 1000thereby to form the second duct section 2000. In another embodiment, thefirst duct section 1000 comprises a screw thread formed at a frontwardend of the first duct section 1000 and the second duct section 2000comprises a corresponding screw thread provided at a rearward end of thesecond duct section 2000. The corresponding screw threads are engageableto attach the first and second duct sections 1000, 2000. In otherembodiments, the second duct section 2000 is formed integrally with thefirst duct section 1000. In this way, the second duct section 2000 isattached to the first duct section 1000 and is supported by the firstduct section 1000.

For the avoidance of doubt, in some exemplary embodiments, a ductsection may only be a region of a larger duct, tube or ring.

The second duct section 2000 comprises a vortex generator surface 3000.Vortex generators are known. Conventional vortex generators areaerodynamic devices, which typically comprise a fixed vane. Conventionalvortex generators are attached to lifting surfaces of aircraft, or toturbine blades.

The vortex generator surface 3000 is arranged to induce vortices in thefluid flow through the first duct section 1000. The vortex generatorsurface 3000 comprises a plurality of projections 3002. The term“projections” is intended to include protrusions, serrations and/orundulations and so on. Each projection has a length 3008 in a lateral,circumferential direction (which may be described as a “wavelength” orportion of a wavelength) and a height 3010 in an axial direction (whichmay be described as an “amplitude”). The projections 3002 project in adirection substantially opposite to the first direction 1006.

In absence of a vortex generator surface 3000, the duct sections 1000,2000 interact with the fluid flow to induce a first set of fluidproperties. The provided vortex generator surface 3000 in the ductarrangement 100 interacts with the fluid flow to induce a second set offluid properties, the second set of fluid properties comprising anincrease in vorticity magnitude of the fluid flow. The vortex generatorsurface 3000 is configured to induce a plurality of periodic, spacedapart vortices, which correspond to the form of the vortex generatorsurface 3000 and the spacing of projections 3002.

The generation of vortices by the vortex generator surface 3000 aid inthe reduction in the vorticity magnitude of the wake produced by boththe interaction of the duct arrangement 100 with the fluid flow and alsoby the interaction of the rotor (not shown) housed therein.Additionally, flow separation on the outer surface of the first andsecond duct sections 1000, 2000 is reduced when compared with a ductedpropulsion unit without a vortex generator surface 3000. Thisadvantageously results in increased thrust production for equivalentenergy input. Overall, this provides for a more efficient propulsionunit, control of the turbulent wake, and a reduction in downstreamvorticity. Furthermore, improved bollard pull performance is obtained,cavitation development is restrained, and underwater radiated noise isreduced.

In the exemplary embodiment illustrated in FIGS. 2 and 3 , the vortexgenerator surface 3000 comprises a series of laterally alignedprojections 3002. The projections 3002 being laterally aligned meansthat they are aligned side-by-side. That is, the projections areadjacent one another. Here, the projections are aligned to form acontinuous surface 3004 having a leading edge 3006. The alignment of theprojections 3002 results in the foremost point of each projection beingaligned in a plane. In this case, said plane is a plane which isperpendicular to the central longitudinal axis of the first and secondduct sections 1000, 2000.

The leading edge 3006 has a continuous wave-like profile, created by therise and fall of the plurality of projections 3002. The terms“wavelength” and “amplitude” used to describe the dimensions of theprojections 3002 are particularly appropriate here. The wavelength isindicated at 3008, and the amplitude is indicated at 3010. Theprojections 3002 are curved along their length such that together theprojections 3002 form a ring of laterally aligned projection 3002 asshown in the figure. It is worth noting that the projections extendaround the circumference of the duct, and not along the duct (e.g. notalong an inner or outer surface of the duct). This may improveperformance, and/or simplify construction.

Referring to FIGS. 4 and 5 , an arrangement 110 is shown. Thearrangement 110 is for installation in an aircraft or watercraft. Thearrangement 110 is for influencing fluid flow. In one exemplaryembodiment, the arrangement 110 is similar in its overall constructionto the duct arrangement 100 described above. That is, the arrangement110 can comprise duct sections. However, the arrangement 110 also findsapplication in sections and flow control surfaces other than ducts.

In the arrangement 110, a first section 1100 is selectively configurableto provide a vortex generator surface 3100. The vortex generator 3100 isprovided to induce vortices in the fluid flow. In one exemplaryembodiment, the fluid flow is a liquid flow (e.g. as opposed to airflow).

The provided vortex generator surface 3100 comprises a plurality ofprojections 3102. The term “projections” is intended to includeserrations and/or undulations. As described above, each projection has alength (which may be described as a “wavelength”) and a height (whichmay be described as an “amplitude”). The projections 3002 project in adirection substantially opposite to a first direction 1106.

In this way, the arrangement 110 is configurable in a configurationwherein the vortex generator surface is not provided, and thereby doesnot interact with the fluid flow to induce vortices therein. Thearrangement 110 is selectively configurable in a configuration whereinthe vortex generator surface 3100 is provided, and thereby interactswith the fluid flow to induce vortices therein. The arrangement 110 isselectively configurable in a configuration wherein the vortex generatorsurface 3100 is provided, to a certain extent or degree (e.g. partially)and thereby interacts with the fluid flow to induce vortices therein toa certain extent or degree. Advantageously, this allows the arrangement110 to be configured to provide the vortex generator surface 3100 whenit is deemed desirable or necessary to induce vortices in the fluid flowusing the vortex generator surface 3100. Advantageously, this alsoallows the vortex generator surface 3100 to be removed, or otherwise notprovided to interact in the fluid flow, which can be beneficial toreduce drag or increase the craft wake where appropriate. These benefitshave, in particular, not been contemplated or realisable in a liquid(e.g. water) environment). This is surprising, given the benefits thatare possible from such an application.

As mentioned above, the provided vortex generator surface 3100 in thearrangement 110 interacts with the fluid flow to induce a second set offluid properties, the second set of fluid properties comprising anincrease in vorticity magnitude of the fluid flow. The vortex generatorsurface 3100 is configured to induce a plurality of periodic, spacedapart vortices, which correspond to the form of the vortex generatorsurface 3000 and the spacing of projections 3002.

The generation of vortices by the vortex generator surface 3100, whenprovided, aid in the reduction in the vorticity magnitude of the wake.Additionally, flow separation on the outer surface of the first andsecond sections 1100, 2100 is reduced when compared with a propulsionunit without an associated vortex generator surface 3100. Thisadvantageously results in increased thrust production for equivalentenergy input. Overall, this provides for a more efficient propulsionunit, control of the turbulent wake, and a reduction in downstreamvorticity. Furthermore, improved bollard pull performance is obtained,cavitation development is restrained, and air/underwater radiated noiseis reduced.

The arrangement 110 further comprises a second section 2100. The firstsection 1100 and second section 2100 are movable relative to one anotherto provide the vortex generator surface 3100.

The arrangement 110 further comprises a controller 112. The controller112 is arranged to implement the selective configuration of the vortexgenerator surface 3100. That is, in this exemplary embodiment, thecontroller 112 controls actuators to extend or expand, or retract orcontract when it is necessary or desirable to provide the vortexgenerator surface 3100. For example, the controller can implement theselective configuration of the vortex generator surface 3100 following:

-   -   a. A user command;    -   b. Input from an additional sensor arrangement 114, for example,        a sensor arrangement operable to measure and detect turbulent        flows, craft velocities and/or fluid flow velocities or the        like; and/or    -   c. Environmental conditions, for example, levels of turbulence,        proximity to other craft, time of day, altitude or the like.

The first section 1100 comprises a resilient membrane 1102 and anactuator assembly 1104. The actuator assembly 1104 is operable to adjustthe profile of the resilient membrane to provide the vortex generatorsurface 3100.

The resilient membrane 1102 is provided in sections across the leadingedge of the second section 2100. The actuator assembly 1104 comprises aplurality of linear actuators, one actuator for each section ofresilient membrane 1102. In the retracted position, the actuators extendback into the second section 2100.

Actuating the actuators causes them to extend away from the secondsection 2100 to contact and force the resilient membrane sections awayfrom the second section 2100, thereby providing a vortex generatorsurface 3100 comprising a series of projections at the leading edge ofthe second section 2100.

Whilst the embodiment described above comprises an actuator assembly1104 and a resilient membrane 1102, other constructions selectivelyconfigurable to provide a vortex generator surface are suitable. Forexample, in one exemplary embodiment, the first section comprises ashape memory alloy, and the application of heat, for example a heatedfluid, causes the shape memory alloy to deform to provide a series ofprojections. In another exemplary embodiment, the first section maycomprise rigid projection members, and a resilient biasing means, orindeed an actuator assembly similar to that described above, can causethe projection members to extend from the second section and/or retractinto the second section.

The advantages of vortex generator surfaces are quantified withreferences to the following non-limited examples provided below. Whilstthe examples provided relate to duct sections, the person skilled in theart will appreciate that similar advantages are obtainable by use of avortex generator surface with other sections, and thus exemplifies thebenefits of both arrangements 100, 110.

FIGS. 6 and 8 show a first duct and propeller interacting with a fluidflow. The duct and propeller are shaped and sized so as to have a firstset of geometrical parameters. The person skilled in the art willappreciate that the geometrical parameters suitable for a duct andpropeller arrangement depends on the specific application and use of thearrangement. The concentric rings surrounding the outside of the duct inFIG. 6 indicate drag induced by the leading edge of the duct. In FIG. 8, a ring-shaped streamwise wake pattern can be seen, indicated by thecontinuous ring surrounding the duct.

FIGS. 7 and 9 show a second duct and propeller interacting with a fluidflow. The second duct and propeller have identical geometricalparameters to the first duct and propeller of FIGS. 6 and 8 . In FIGS. 7and 9 , in addition to the duct and propeller, a vortex generatorsurface is provided at the leading edge of the duct.

As can be seen in FIG. 7 , regions of drag are compartmentalised atperiodic intervals about the circumference of the duct. This is due tothe provision of the vortex generator surface. As a result, this createsless overall drag when compared with the duct and propeller ofExample 1. In this example, there is a 50% reduction in total drag.

As can be seen in FIG. 9 , counter rotating streamwise vortices areinduced by the vortex generator surface, whereas they were not inExample 1 above. As can be seen in the figure, the vortices arespatially separated, i.e. spaced apart, about the circumference of theduct. That is, the vortex generator surface is configured to induce aplurality of spaced apart vortices. The vortices induced are periodic.

The induced vortices aid in the reduction in the magnitude of the wake.Comparing FIGS. 6 and 7 , whilst the duct is shown to interact with thefluid flow, resulting in a first set of fluid properties (for example, afirst wake pattern), the vortex generator surface interacts with thefluid flow to induce a second set of fluid properties (for example, asecond wake pattern). As shown in FIG. 9 , the second set of fluidproperties may include an increase in the vorticity magnitude of thefluid flow, which surprisingly reduces the vorticity magnitude of thewake.

Additionally, flow separation on the outer surface of the duct inExample 2 is lower than that of Example 1, as a result of the provisionof the vortex generator surface. This advantageously results inincreased thrust production for equivalent energy input. Overall, thisprovides for a more efficient propulsion unit, control of the turbulentwake, and a reduction in downstream vorticity. Furthermore, improvedbollard pull performance is obtained, cavitation development isrestrained, and underwater radiated noise is reduced.

Referring to FIG. 10 , a method of guiding fluid flow is shown. StepS1000 comprises generating vortices in a fluid flow using a second ductsection comprising a vortex generating surface. Step S1002 comprisesreceiving the fluid flow in a first duct section.

Referring to FIG. 11 , a method of influencing liquid flow in anarrangement comprising a first section selectively configure to providea vortex generator surface is shown. Step S2000 comprises configuringthe first section to provide the vortex generator surface to inducevortices in the liquid flow.

Referring to FIG. 12 , a method of influencing fluid flow in anarrangement comprising a first section selectively configurable toprovide a vortex generator surface comprising a series of laterallyaligned projections is shown. Step S3000 comprises configuring the firstsection to provide the vortex generator surface to induce vortices inthe fluid flow.

The apparatus described herein could be made or manufactured as acompletely new, standalone entity in certain examples. However, at leastsome implementations could be readily retrofitted to realise the aboveadvantages, for example retrofitting a vortex generator surface asdiscussed herein, to an existing flow influencing surface or object, ormoving an existing vortex generator surface to a different location, andso on.

As above, it will be appreciated that the aspects and embodiments areclosely linked and interrelated, and different features of any oneaspect or embodiment could sometimes be used in addition with, on inplace of, a feature of another aspect or embodiment.

Although a few preferred embodiments of the present invention have beenshown and described, it will be appreciated by those skilled in the artthat various changes and modifications might be made without departingfrom the scope of the invention, as defined in the appended claims.

The preceding description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the preceding description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.The terms “front”, “rear”, “side”, “upper”, “lower”, “over”, “under”,“inner”, “outer” and like terms are used to refer to the apparatus andits components in the orientation in which it is illustrated, which isthe orientation in which it is intended to be used but should not betaken as otherwise limiting. Like reference numerals are used to denotelike features throughout the figures, which are not to scale.

At least some of the example embodiments described herein may beconstructed, partially or wholly, using dedicated special-purposehardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein mayinclude, but are not limited to, a hardware device, such as circuitry inthe form of discrete or integrated components, a Field Programmable GateArray (FPGA) or Application Specific Integrated Circuit (ASIC), whichperforms certain tasks or provides the associated functionality. In someembodiments, the described elements may be configured to reside on atangible, persistent, addressable storage medium and may be configuredto execute on one or more processors. These functional elements may insome embodiments include, by way of example, components, such assoftware components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. Although the example embodiments have been described withreference to the components, modules and units discussed herein, suchfunctional elements may be combined into fewer elements or separatedinto additional elements. Various combinations of optional features havebeen described herein, and it will be appreciated that describedfeatures may be combined in any suitable combination. In particular, thefeatures of any one example embodiment may be combined with features ofany other embodiment, as appropriate, except where such combinations aremutually exclusive. Throughout this specification, the term “comprising”or “comprises” means including the component(s) specified but not to theexclusion of the presence of others.

Attention is directed to all papers and documents which are filedconcurrently with or previous to this specification in connection withthis application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1. An arrangement for influencing liquid flow, the arrangementcomprising: a section selectively configurable to provide a vortexgenerator surface to induce vortices in the liquid flow.
 2. Thearrangement according to claim 1, wherein the section is a firstsection, the arrangement further comprising: a second section, whereinthe first section and second section are movable relative to one anotherto provide the vortex generator surface.
 3. The arrangement according toclaim 2, wherein the first section is movable away from and/or towardthe second section.
 4. The arrangement according to claim 2, wherein thefirst section is selectively configurable to provide the vortexgenerator surface at a leading edge of the second section.
 5. Thearrangement according to claim 2, wherein the second section comprises aflow control surface.
 6. The arrangement according to claim 1, furthercomprising a controller arranged to implement the selectiveconfiguration of the vortex generator surface.
 7. The arrangementaccording to claim 6, wherein the controller is arranged to implementthe selective configuration of the vortex generator surface independence upon: a user command, input from a sensor arrangement, and/orone or more environmental conditions.
 8. The arrangement according toclaim 1, wherein the section is selectively configurable to change theshape of the arrangement, thereby to provide the vortex generatorsurface to induce vortices in the liquid flow.
 9. The arrangementaccording to claim 1, wherein the section is selectively configurable tochange the shape of the vortex generator surface, thereby to provide thevortex generator surface to induce vortices in the liquid flow.
 10. Thearrangement according to claim 1, wherein the section is selectivelyconfigurable in: a first configuration wherein the vortex generatorsurface is provided to induce vortices with a first property in theliquid flow; and a second configuration wherein the vortex generatorsurface is provided to induce vortices with a second property in theliquid flow.
 11. The arrangement according to claim 10, wherein thesecond property is greater than the first property.
 12. The arrangementaccording to claim 1, wherein the section is selectively configurable toprovide a vortex generator surface comprising a series of projections.13. The arrangement according to claim 1, wherein the section isselectively configurable to provide a vortex generator surface to inducea plurality of spatially separated vortices in the fluid flow, whereinthe spatially separated vortices may include periodic vortices.
 14. Awatercraft comprising the arrangement according to claim
 1. 15. A methodof influencing liquid flow in an arrangement comprising a first sectionand second section, the first section selectively configurable toprovide a vortex generator surface, the second section including a flowcontrol surface, wherein the first section and second sections aremovable relative to one another to provide the vortex generator surface,the method comprising: moving the first section and the second sectionrelative to one another to provide the vortex generator surface toinduce vortices in the liquid flow.
 16. The arrangement according toclaim 3, wherein the first section is extendable from and/or retractableinto the second section.
 17. The arrangement according to claim 5,wherein the flow control surface includes a rudder, a duct, and/or arotor.
 18. The arrangement according to claim 2, wherein the secondsection is a flow control surface.
 19. The arrangement according toclaim 11, wherein the first property is a magnitude of zero and thesecond property is a non-zero magnitude, or wherein the first propertyis a non-zero magnitude and the second property is a greater non-zeromagnitude.
 20. An arrangement for influencing liquid flow, thearrangement comprising: a first section selectively configurable toprovide a vortex generator surface to induce vortices in the liquidflow; and a second section including a flow control surface; wherein thefirst section and second section are movable relative to one another toprovide the vortex generator surface.